Perfecting the DDGS Pellet
Pelletizing distillers dried grains with solubles can be more art than science. Past attempts at pelletizing 100 percent DDGS have fallen short. Rising to the challenge, Ag Fuel & Feed LLC says it has manufactured a pellet die that will extrude a 100 percent DDGS pellet without additives or binders.
After consulting with scientists at a few agricultural universities, Wobler was given a list of companies that pelletize agricultural products for feed. At the top of the list was Ft. Worth, Texas-based Landers Machine Co.
"Gary just happened to call me first and asked if I thought it could be done," says Scott Landers, president of Landers Machine. "I said we have quite a background in [pelletizing] and I'll talk it over with some of my engineers and we'll see if we can do it.
"We started kicking some things around and decided that we would go ahead and give it a shot," he says, "and so we started our research to try to develop this process and, after probably four months of testing, we had a pretty good feeling that we would achieve something. At that point, we decided that [Landers Machine and Ag Pellet Energy] would form Ag Fuel & Feed."
Landers says Ag Fuel & Feed LLC has overcome the technical challenges associated with pelletizing 100 percent DDGS without using additives or binders. The key to their engineering success has been to design a pellet mill die that has been specifically engineered for pelletizing DDGS. "(After forming Ag Fuel & Feed), it took us probably another nine months of research and then testing and modifications until we actually came up with the process," Landers said. The production process was developed and test-runs were completed at the Waterloo Mills Co. in Waterloo, Iowa, funded in part by a $49,380 Grow Iowa Values Fund grant through Iowa State University.
One of the baseline measurements for determining the quality of a pellet is the pellet durability index (PDI), which is determined by tumbling pellets for a period of time to find the volume of fines produced. "We like to see a pellet with a pellet durability index of 92 percent or better," says Alan Doering, associate scientist of co-products at the Agricultural Utilization Research Institute office in Waseca, Minn., which has been testing to see how U.S. energy crops can be made into pellets for combustion. "You can make pellets that are 99 percent durable," he says, "but then you typically sacrifice throughput in terms of tons per hour."
Achieving a durable pellet using DDGS is difficult. Comparing figures provided by animal scientists at Ohio State University with information from Encyclopedia Britannica, DDGS has four to nine times less lignin content than varieties of wood. In general, the lower lignin content of non-woody biomass gives it less tensile and compressive strength, according to French agronomist Olivier Pastré in a report for the European Biomass Industry Association.
"In the past, you might get [DDGS] to produce a pellet," Landers says, "but it would have no hardness or a very low PDI and, in handling, they would just completely fall apart, even going from the pellet mill to the cooler."
Landers says DDGS has been successfully used as an additive for feed pellets, "but you're talking somewhere between 25 and 45 percent addition there," he says. "Anytime they get any higher than that, they just can't maintain the pellet."
After months of work, however, Landers says he and his engineers have mastered pelletizing 100 percent DDGS to produce a pellet with a high PDI. The Ag Fuel & Feed pellet has a
PDI of 94 percent, he says, compared to a 72 percent average using traditional pelletizing technologies. Wood pelletizes at a 96 percent average PDI.
"The biggest challenge that has to be overcome is the oil content," Landers says. "With about eight percent oil still remaining in the granular DDGS, it poses a significant problem to conventional [pelletizing] operations. That's just too much oil to keep bound in a pellet, even a small pellet.
"The product is too slippery, too moist, and the oil works against the actual process of holding and compacting the pellet together and then having it stay together," he continues. "The oil lubricates it so that the granules won't stay together. In our patent-pending process, we have taken measures to overcome having that amount of oil and, in a way, use it to our advantage to actually help us to make the pellet."
The market for DDGS is global and plants typically sell two-thirds of distillers grains dried, but the drying process can consume about 30 percent of the plant's operating budget.
Meanwhile, shipping DDGS to international markets using a combination of rail, containers and barge has led to transportation costs becoming the third-highest expense for ethanol producers after feedstock and energy costs, according to Frank Dooley, an agronomist at Purdue University in West Lafayette, Ind., and Bobby Martens, a logistician at Iowa State University.
Meanwhile, the industry continues to address DDGS flowability issues. Dooley and Martens note that DDGS that has moisture content higher than 10 percent can solidify during shipment, forcing load operators to hammer the sides and bottoms of hoppers to induce flow. This has led railroads to require DDGS to be shipped in hopper cars owned or leased by the shipper. (There was a 25,000-unit increase in demand for jumbo hoppers between 2005 and 2007, Dooley and Martens say.)
Dooley and Martens published their observations in an electronic book titled "Using Distillers Grains in the U.S. and International Livestock and Poultry Industries" published by the Midwest Agribusiness Trade Research and Information Center at ISU.
If ethanol producers were to pelletize DDGS before shipping them, the increased bulk density of the pelletized DDGS would result in transportation cost savings and would alleviate DDGS flowability issues. Landers says Ag Fuel & Feed can produce a pellet with a bulk density of 40.6 pounds-per-cubic-foot, 28 percent more dense than un-pelletized DDGS, and the pellets flow "like corn," he says, better than unpelletized DDGS. Pelletized DDGS might help to open export markets where customers are having difficulty unloading and transporting bulk products, especially DDGS, Landers says. "[Pelletizing] facilitates handling problems," he says, "because [the pellets] flow much better in screw conveyers and bucket elevators and they would be able to unload rail cars much more easily.
"If [ethanol producers] would take a hard look at what savings could be achieved in transportation and handling, I think that our product starts to look better and better," Landers says.
John Fox, an agronomist at Kansas State University in Manhattan and a contributor to the MATRIC publication, says that to expand export markets, the ethanol industry needs to address product variability issues. One way to do that is to sell DDGS as a branded product. An individual ethanol producer might also consider pelletizing its DDGS to differentiate the co-product from others.
Landers says cattle producers might see more value in pelletized DDGS. "Pellets in a feedlot are going to be easier for the cows to consume and to consume fully than when they are dealing with mash," Landers says. "When they are having mash thrown in those trays, then they slop a lot of it around. Pellets are just easier to consume."
DDGS Pellets for Fuel
As more U.S. states and Canadian provinces adopt or increase renewable portfolio standards for electrical utilities, more power companies are looking at burning biomass pellets in coal-fired boilers. AURI has seen a continual growth in interest from industries for pelletizing non-woody biomass over the past six years, spurred in part by sporadic increases in wood prices, Doering says. "[They are] looking at pellet fuels to displace natural gas," he says, "or looking at densified solid fuels to cofire with coal. We're working with some utilities, investigating that potential."
Pastré notes that the fluidized bed combustion technology used at power plants is inherently flexible and can burn fuels with a wide range of calorific values, ash and moisture content and they have successfully been used to co-fire wood, biomass and waste materials, in addition to coal.
Ag Fuel & Feed has been working with power companies to test burn DDGS pellets with coal. A mixture of 10 percent DDGS pellets was co-fired with coal at Corn Belt Power Cooperative's Wisdom Station power plant near Spencer, Iowa. Burning a mixture of pellets at 8,400 British thermal units per pound with bituminous coal averaging 10,500 Btu, the test resulted in visually clearer smoke from the plant's stack. "They visually saw an improvement in the opacity of the emissions from the stack," Landers says, "and that is what was most interesting and significant to them."
Before power companies can use biomass pellets on a regular basis, they must address emissions issues. Pastré notes that compared with wood, agricultural residues typically have higher nitrogen, sulfur, chlorine and potassium content due to increased use of fertilizers, pesticides and herbicides in agriculture. He says agro-pellets should primarily be used in large-scale combustion plants equipped with sophisticated combustion control and flue gas cleaning systems. In a report for Pellets Atlas, dubbed pellets@las, an Intelligent Energy Europe-funded project for the European Union, Martin Junginger, a researcher at Utrecht University in The Netherlands, notes that unknown emissions from biomass pellets is one of the major factors preventing the development of a larger, non-woody biomass pellet market.
Landers says while emissions from burning DDGS pellets alone have been quantified, further tests are planned to check the emissions levels when DDGS pellets are co-fired with coal.
"Right now, we are working with several different cooperatives in trying to get some more testing (completed) and to get the EPA involved to actually get some tangible figures on the emissions," Landers says. "If we can get some hard facts, then that would give us some more ammunition to go out to other cooperative generating plants to say that by blending this product, you will see X amount in carbon dioxide emissions."
Landers says Ag Fuel & Feed hired a consultant to quantify the lifecycle carbon dioxide emissions from burning DDGS pellets as fuel to generate electricity. The report determined burning DDGS pellets contributes 38 to 77 times less carbon dioxide than coal on a per-unit basis, even without factoring in the additional carbon dioxide generated from mining and transporting coal to the power plant.
The test burn at Wisdom Station also resulted in slightly less power generation, which was expected. "They ran a two-hour test and they did see some drop in efficiency at the plant," Landers says, "just because the coal they were using had about 10,500 Btu per pound, but that was expected, given our Btus." Landers says the 8,400 Btu measurement is on the low end of the varying Btu amounts DDGS pellets might produce. "We got several different Btu contents from several different batches," he said, "and I'd rather under-promise and overachieve."
Ryan C. Christiansen is the assistant editor of Ethanol Producer Magazine. Reach him at firstname.lastname@example.org or (701) 373-8042.